Disk tray mechanism for reproducing apparatus

ABSTRACT

The invention relates to a tray mechanism consisting of sliding means comprising an electrical tray motor, for moving a tray—provided for containing a disc (for example an optical disc) on which information is recorded—from a projected position, for the placement of the disc or its discharge, to a contained one, for the reproduction of recorded information, or reciprocally, and a drive power source, for supplying an applied voltage to said tray motor. Control means supply different values of the voltage applied to the tray motor according to different mechanical functions controlled by said motor. According to the invention, it is provided, for the tray steering, a motor current feed-forward loop comprising a first direct branch, itself comprising in series a first amplifier of the input voltage applied to the loop, the tray motor and a resistor, and a second branch, itself comprising in series a second amplifier and an adder, which receives on one input the input voltage applied to the loop and on the other one the output of said second amplifier.

FIELD OF THE INVENTION

The present invention first relates to a tray mechanism consisting ofsliding means comprising an electrical tray motor, for moving atray—provided for containing an optical disc on which information isrecorded—from a projected position, for the placement of the disc or itsdischarge, to a contained one, for the reproduction of recordedinformation, or reciprocally, and a drive power source, for supplying anapplied voltage to said tray motor, said sliding means also includingcontrol means for supplying different values of the voltage applied tothe tray motor according to different mechanical functions controlled bysaid motor.

The invention also relates to a reproducing apparatus comprising anapparatus body, pickup means for optically picking up recordedinformation from a disc and a tray mechanism for sliding said disc, withrespect to said apparatus body, either to a projected position, for theplacement of the disc or its discharge, or to a contained position, forthe reproduction of recorded information, said tray mechanism consistingof sliding means comprising an electrical tray motor and a drive powersource for supplying an applied voltage to said tray motor, said slidingmeans also including control means for supplying different values of thevoltage applied to the tray motor according to different mechanicalfunctions controlled by said motor.

The invention is for instance applicable in a CD or DVD drive, thisapplication being however not a limitation of the scope of theinvention.

BACKGROUND OF THE INVENTION

A commonly used mechanism for loading a disc in a disc drive is that ofa tray mechanism: the tray is either in an “OUT” position, in which thedisc can be placed on it or taken out, or in an “IN” position, in whichthe disc is loaded in the drive and can be pushed out or pulled back byan electrical direct current motor. For moving the tray out or in, avoltage is applied to the motor for a specified amount of time. Duringthis time, this voltage can have different values at different moments,first to create a smooth motion of the tray, and also because the traymotor has to control other mechanical functions of loading or unloadingthe disc (for example an extra force is needed when the magnetic clamperhas to release the disc).

With the applied voltages, the tray must move out and in within aspecified time. It is then important that the electrical and mechanicalspecifications of the tray mechanism are known within small tolerancesand do not change during its lifetime. If the specifications do not meetthe applied voltages, this would result in a too fast or too slow traymovement. In worst case situations, the tray could even not move at all,for example when the friction of the tray has increased because ofcontamination.

SUMMARY OF THE INVENTION

It is a first object of the invention to improve the performance of theDC tray motor, so that the specifications of the tray mechanism bettermeet the voltages applied to the motor.

To this end, the invention relates to a tray mechanism as defined in theintroductory part of the description and which is moreover characterizedin that said sliding, means includes a motor current feed-forward loopcomprising the following elements:

a first direct branch, itself comprising in series a first amplifier ofthe input voltage applied to the loop, the tray motor and a resistor;

a second branch, the input of which is connected between the output ofthe tray motor and the input of the resistor that is not connected tothe earth, said second branch itself comprising in series a secondamplifier and an adder, and said adder receiving on one input the inputvoltage applied to the loop and on the other one the output of saidsecond amplifier.

The document U.S. Pat. No. 6,373,650 describes a linear motor controlcircuit used for moving according to several operating modes theread/write heads of memory disc drives. The driver circuit of the linearmotor includes a non-linear feedback circuit, and this circuit comprisesa sense amplifier, followed first by a ramping amplifier, and then by afeedback amplifier. The ramping amplifier is either connected in serieswith the sense amplifier in a first head parking/unparking mode ofoperation, for modifying the signals from the sense amplifier, orbypassed in the other modes. The feedback amplifier is connected eitherto the output of said ramping amplifier in the first mode or to theoutput of said sense amplifier in the other modes and switched toprovide either a first predetermined gain in said first mode or anotherpredetermined one in the other modes. The selective connection of theramping amplifier according to the operating mode allows to change thesign of the feedback and therefore to drive the motor as a function ofeither a positive or a negative feedback signal. With respect to thatsolution, the technical one according to the present invention ishowever much simpler and allows to achieve a linear and closer controlof the speed of the motor.

It is another object of the invention to propose a reproducing apparatus(for instance an optical disc reproducing apparatus) in which such amechanism is provided.

To this end, the invention relates to a reproducing apparatus as definedin the introductory part of the description and which is moreovercharacterized in that the sliding means include a motor currentfeed-forward loop comprising the following elements:

a first direct branch, itself comprising in series a first amplifier ofthe input voltage applied to the loop, the tray motor and a resistor;

a second branch, the input of which is connected between the output ofthe tray motor and the input of the resistor that is not connected tothe earth, said second branch itself comprising in series a secondamplifier and an adder, and said adder receiving on one input the inputvoltage applied to the loop and on the other one the output of saidsecond amplifier.

With respect to an open loop steering of the motor, it appears that,with the technical solution according to the invention, the velocity ofthe motor is less dependent of friction (that can differ from onemechanism to the other and generally increases during lifetime becauseof contamination). Moreover, said velocity, based on a measured orspecified motor constant of the tray motor, can be controlled quiteaccurately and is more independent from other parameters. The velocitybeing better controlled, a much smoother opening and closing of the trayis possible, no overcompensation of the voltage is needed to handletolerances of the tray mechanism, and a better timing is possible, forexample for reducing the velocity of the tray when it is about to hit anend stop.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, in a moredetailed manner and with reference to the accompanying drawings, inwhich:

FIG. 1 illustrates the main elements of an apparatus for reproducingrecorded information;

FIG. 2 shows the motor current feed-forward principle according to theinvention;

FIG. 3 shows the model used for the tray motor.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, an apparatus for reproducing information recorded ona disc, for example an optical disc, usually comprises the mainfollowing elements: an apparatus body 11, pickup means 12 for opticallypicking, up recorded information from an optical disc rotated by a motor(not referenced) and a tray mechanism 13 for moving a tray containingsaid disc either to a so-called projected position A (with respect tosaid apparatus body 11), for the placement of the disc in view of thereproduction of recorded information or its discharge when saidreproduction is brought to its end, or to a so-called contained positionB, in which the reproduction operation can be carried out. The traymechanism 13 itself consists of sliding means mainly composed of anelectrical tray motor 14 and a drive power source 15 for supplying anapplied voltage to the tray motor 14, said sliding means also includingcontrol means for supplying different values of the voltage applied tothe tray motor according to different mechanical functions selectivelycontrolled by said motor at different moments (for example, an extraforce is needed when the disc has to be released).

According to the invention, it is proposed to provide in the slidingmeans, for the tray steering, a current feed-forward loop. The diagramof FIG. 2 shows the principle of such a motor current feed-forward loop,which includes a direct branch 21 and a feedback branch 22. The branch21 successively comprises an amplifier 211 (reference G in FIG. 1), atray motor 212 and a resistor 213 (reference R_(c)). The branch 22, theinput of which is connected between the output of the tray motor and theinput of the resistor 213 not connected to the earth, successivelycomprises an amplifier 221 (reference A) and an adder 222. The adder 222receives on one input the input voltage V(in) applied to the loop and onthe other input the output of the amplifier 221 and its output isconnected to the input of the amplifier 211.

For the tray motor, a very simple model is used. As shown in FIG.3, saidmodel contains a self-inductance 31 of the coils, an internal resistance32 (R_(M)) and a voltage source 33 V_((EMK)) that represents the backelectromotive force generated by the coil of the motor. This model caneven be simplified by assuming that the signals applied to the motor areof relatively low frequencies (in this situation, the influence of theself-inductance of the coils can be ignored) and that the voltageV_((EMK)) of the voltage source 33 is a quasi-static signal that isproportional to the angular velocity of the motor.

From these assumptions, in order to show what influence the currentfeed-forward loop has on the behaviour of the motor in relation to thevoltage applied to the system, the loop transfer can be calculated. Theoutput voltage of the motor driver equals:V(out)=G·(V(in)+A·V(C))  1)with:

G=gain of the amplifier 211;

V(in)=input voltage applied to the loop;

A=gain of the amplifier 221;

V(C)=voltage at the output of the resistor 213 not connected to theearth.

The expression (1) also be written:V(out)=G·(V(in)+A·i(M)·R _(c))  (2)with i(M)=current through the resistor 213 (R_(c)), or:V(out)=i(M)·(R _(c))+R(M))+V _((EMK))  (3)By combining the expressions (2) and (3), one gets the followingexpression:i(M)·(R(C)+R(M))+V _((EMK)) =G·(V(in)+A·i(M)·R _(c))  (4)which can also be written in the form:G·V(in)=V _((EMK)) +i(M)·(R _(c) +R(M)−G·A·i(M)·R _(c)  (5)So, if the gain is chosen in the feed-forward loop with the value:A=(R _(c) +R(M)/(G·R _(c))  (6)Then the expression (5) becomes:G·V(in)=V _((EMK))  (7)In this expression (7), it can be seen that the feed-forward loop actsas a negative resistance that compensates for the motor resistance RM.As said above, the back electromotive force V_((EMK)) of the motor isproportional to the angular velocity of the motor. So, from theexpression (7), it can be concluded that by choosing the correctfeed-forward gain, the tray motor can be forced to have an angularvelocity that is proportional to the input voltage V(C).

In practice, the effect of the feed-forward is slightly reduced becauseof the fact that the gain cannot be set exactly to the calculated value.Tolerances in the system and changing characteristics because of agingcould indeed result in a gain that is higher than the calculatedoptimum, which may result in a less stable loop. When working with afixed gain, the gain has therefore to be chosen conservatively low (amore complex method would be using the current measurement for measuringthe characteristics of the loop and, based on this measurement,selecting the gain more accurately, which improves the performance ofthe feed-forward loop).

It has been shown that the loop structure according to the inventionresults in a tray motor behaviour that comes close to a velocitycontrolled steering and has the advantages indicated hereinabove.

1. A tray mechanism consisting of sliding means comprising an electricaltray motor, for moving a tray—provided for containing a disc on whichinformation is recorded—from a projected position, for the placement ofthe disc or its discharge, to a contained one, for the reproduction ofrecorded information, or reciprocally, and a drive power source, forsupplying an applied voltage to said tray motor, said sliding means alsoincluding control means for supplying different values of the voltageapplied to the tray motor according to different mechanical functionscontrolled by said motor, wherein said sliding means includes, for thetray steering, a motor current feed-forward loop comprising thefollowing elements: a first direct branch, itself comprising in series afirst amplifier of the input voltage applied to the loop, the tray motorand a resistor; a second branch, the input of which is connected betweenthe output of the tray motor and the input of the resistor that is notconnected to the earth, said second branch itself comprising in series asecond amplifier and an adder, and said adder receiving on one input theinput voltage applied to the loop and on the other one the output ofsaid second amplifier.
 2. A disc reproducing apparatus comprising anapparatus body, pickup means for picking up recorded information from adisc and a tray mechanism for sliding said disc, with respect to saidapparatus body, either to a projected position, for the placement of thedisc or its discharge, or to a contained position, for the reproductionof recorded information, said tray mechanism consisting of sliding meanscomprising an electrical tray motor and a drive power source forsupplying an applied voltage to said tray motor, said sliding means alsoincluding control means for supplying different values of the voltageapplied to the tray motor according to different mechanical functionscontrolled by said motor at different moments, wherein said slidingmeans includes, for the tray steering, a motor current feed-forward loopcomprising the following elements: a first direct branch, itselfcomprising in series a first amplifier of the input voltage applied tothe loop, the tray motor and a resistor; a second branch, the input ofwhich is connected between the output of the tray motor and the input ofthe resistor that is not connected to the earth, said second branchitself comprising in series a second amplifier and an adder, and saidadder receiving on one input the input voltage applied to the loop andon the other one the output of said second amplifier.